Optical scale reading device for rotatable dividing tables



p 1951 c. F. DIETRICH ET AL 2,566,875

OPTICAL SCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES Filed Jan.14, 1949 7 Sheets-Sheet 1.

INYCNTO R 5 Sept. 4, 1951 C. F. DlETRlCH ET AL OPTICAL SCALE READINGDEVICE FOR ROTATABLE DIVIDING TABLES 7 Sheets-Sheet 2 Filed Jan. 14,1949 Sept. 4, 1951 c. F. DIETRICH ET AL 2,566,875

OPTICAL SCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES Filed Jan.14, 1949 '7 Sheets-Sheet 5 4 2 44 a4 63" EW Sept. 4, 1951 c. F. DIETRICHET AL 2,565,875

' OP T ICAL SCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES FiledJan. 14, 1949 7 Sheets-Sheet 4 2a- 29 1/4 10 A //1\m\ 0 I I I 6/3 219 2p 4, 1951 r c. F. DlETRlCH ET AL 2,566,875

OPTICAL SCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES Filed Jan.14, 1949 v Sheets-Sheet 5 Sept. 4, 1951 c. F. DIETRICH ET AL 5 OPTICALSCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES Filed Jan. 14, 1949 7Sheets-Sheet 6 ZNveJvToRs p 1951 c. F. DIETRICH ET AL 2,566,875

OPTICAL SCALE READING DEVICE FOR ROTATABLE DIVIDING TABLES 7Sheets-Sheet '7 Filed Jan. 14, 1949 w ew kw INVQNT'OR'S Maw JIVIIAI' vwn m, m.- a

RAP ///////4 w Nob 3 Patented Sept. 4, 1951 OPTICAL SCALE READING DEVICEFOR ROTATABLE DIVIDHNG TABLES Cornelius Frank Dietrich and Harry JohnSmith,

Slough, England, assignors to Optical Measuring Tools Limited, Slough,England, a British company Application January 14, 1949, Serial No.70,892 In Great Britain January 14, 1948 6 Claims.

This invention relates to rotatable dividing tables for rotary indexing,such as are used with jig borers, horizontal borers, grinding machinesand vertical and universal millers.

Some constructions of circular dividing table incorporate a microscopeas an aid to the accurate reading of a circular degree scale on thetable. But the use of a microscope has the disadvantage that sightingthrough the eyepiece is inconvenient and liable to produce eyestrain.The main object of the present invention is to provide an improvedcircular dividing table having measuring means for accuratelydetermining to close limitsthe angular setting of the table andpermitting the reading with facility of this setting. A further featureof the invention. consists of control means for accurate setting of thetable.

According to the present invention, in a rotatable dividing table havinga graduated circular scale rotatable with the table and located beneathit in a supporting base, there is provided an illuminant in the base forthe circular scale, a fixed optical projecting system adjacent to theilluminated portion of the circular scale and a projection screen at theside of the base on to which the projecting system throws a magnifiedimage of the said portion of the circular scale.

Preferably the optical system comprises a light source for illuminatingthe portion of the circular scale, an objective lens system formagnifying the image of said portion to the desired size and a lenssystem comprising a projector for throwing the magnified image onto thescreen. Preferably in a rotatable dividing table measuring means fordetermining the angular setting comprise in combination a graduatedcircular scale mounted concentrically with the table for rotationtherewith, an optical projecting system for projecting an image of aportion of the scale, a screen to display said image and means forsuperimposing on the image on the screen a reference scale having arange of one division of the circular scale and of the same size as theprojected image thereof, but having subdivisions against whichintermediate positions of the circular scale can be read. The referencescale may be engraved on a transparent grating interposed in the opticalpath to the projection screen in such manner that an image of thereference scale is projected on to the scsreen together with the imageof the circular scale. Preferably there is interposed in the opticalprojecting system a movable subdivided scale, also projected upon thescreen, so connected to means formoving the 2 image of the circularscale as to move ata constant high velocity ratio relatively thereto,and an index forreading movements of the movable scale so that smallmovements of the circularscale image can be exactly ascertained byreading the larger movements of the said movable scale.

The prism system and a projector lens may be together mounted on a maincradle which is laterally adjustable relative to an objective lenssystem located between the circular scale and the cradle so as to permitmoving the image of the grating relatively to the image of the circularscale thereby facilitating reading the table setting on the screen; andin which the prism system is mounted on a sub-cradle which is carried bythe first and is laterally adjustable relatively thereon to permitmoving the graticule image into a desired position relatively to thegrating image. Locking means may be provided which permit holding themain cradle in a desired lateral position relative to the objective lenssystem, and locking means are provided which permit holding thesub-cradle in a desired lateral position relative to the main cradle.

The table control means for effecting rotation and setting of the tablemay comprise a worm and worm-wheel drive for the table, and a two.-speed epicyclic gear for driving the shaft from a hand control, therebeing a direct drive to the worm shaft from the hand control to thewormgearing and an indirect drive with speed-reduction through theepicyclic gear. Locking means may be provided for holding the tableagainst rotation in its set position, and also the worm may be arrangedso that it can be disengaged from the worm-wheel and thereby permit freerotation of the table by hand for rough adjustment to the angularsetting.

lhe following is a description, by way of example, of one constructionQfcircular dividing table according to the present invention, referencebeing made to the accompanying drawings in which:

Figures 1A and 1B show a table top in plan with portions broken away toshow the interior.

Figure 2 shows a vertical section through line 2-2 of Figures 1A and 113as seen as a right projection.

Figure 3 shows a lighting-unit in vertical section through line 3-3 ofFigure 1B, and

Figure 4 shows the unit and a locking device in elevation taken throughline 4--4 of Figure 1B.

Figure 5 shows an optical system in vertical section through line 22 ofFigure 1B and Figure 6 shows itscasing broken away to show of a prismsystem and controls.

Figure '7 shows diagrammatically an optical path of a ray from thelighting unit to a screen.

Figures band 9 show a drive in vertical section through line 8:8 ofFigure 1A, in two -p osi,.- tions.

Referring to Figures 1A, 1B and 2, a circular dividing table 10 ismounted for rotation on a bearing surface II at the top Of a circularbase casting [2. At the centre of and beneath, the table II] is fixed avertical pivot it which is mounted for rotation in bearings It withinaboss on the base I2. Between the table it and base l2 the pivot itcarries a flange It. A graduated circular scale Showing degrees isaiforded by a clear-glass annulus i1 secured by a clamping ring l8 tothe perimeter of the flange 15 so as to rotate concentrically with thetable It The upper face of the glass annulus ll bears a transparent ring19 engraved with opaque degree lines and numerals ranging from 0 to 359.

Referring to Figures 113, 3 and 4, a tubular lighting unit 20' forilluminating a small segment of the glass annulus l-"i is located in ahorizontal passage 2| within the base Hi. This passage 2! extends froman opening 22 (see Figure 13) at the base pg meter to a vertical bore 23in the base l2 whose axis lies a little outside the perimeter oi theglass annulus I1. The lighting unit 20 can be withdrawn for replacementthrough the opening in the base E2. The vertical bore 2-3 at the innerend of the lighting unit 20 is fitted with a tubular housing 25 for arhomb prism 26. At its upper end 21', the housing 25 carries alateralextension 28 which projects over the upper face of the glass annulus llso that a beam of light can be directed normally on to the ring I8. 7

The prism housing 25 is made rotatable in its bore 23 so that theextension 28 can be swung out clear of the annulus I? for removal andreplacement of the annulus during assembly. In order to prevent damageto the annulus I! by the extension 28, a locking device Hi, shown inFigures 1B and 4 is fitted in the base l2 to prea plan vent movement ofthe table It and annulus l1 until the extension 28 is swung clear. Thisdevice Ill consists of a double-armed roclsinga lever pivoted about'avertical axis in the base I2. A lower arm H2 of the lever has adependent pin H3 which engages a slot H5 in the prism housing 251 toform afp-inaandeslot connection therewith such that'rotation of thehousing 25 causes a rocking movement of the lever Ill.

The upper end of the lever Hi is in the form of a tongue, I l 5 formoving in and out of an annular I0 is freed for removal. The tongue H5also acts as a stop to prevent replacement of the'table l0 and housing25 while the housing extension 28 is in its overlying position.

Thelighting unit 20 contains an electric lamp 30 connected to a supplycable 3! running out through the outer end 32 of the unit 20. Figure I 3shows how light from thelamp 30 is projected through condenser lenses 33at the inner end 2.4 of the 'unit zfl' into the tubular prism nous,

ing 25 through a side'opening 34 therein. The tubular housing 25 isfitted with a rhomb prism 25 by means of which a light beam from thelamp 55 is reflected up the housing 25 and thence inwards oi the tableIt through a side opening 54 at the, upper end of the extension 23. Inthe end of the extension 28 are a lens35 andprism .35, and light isdeflected downwardly through a portion of the ring [9 and glass annulusl1.

Referring more particularly to Figure 5, under the glass annulus I!immediately below the extensiongt on the prism housing 25 is an inclinedmirror 31 at theflinner end of a tube 58 containing an objective lenssystem 59 for magnifying the portion of the annulus projected by thelamp 3!]. The'objective lens tube 38 is fittedin a radial passage 59within the base i2 (Figure 2). The

tube 33 carries on its outer end a bracket 4! lo-' cated at the back ofa casing 42 fitted on the front of the base i2. In the casing 42 ismounted a ubrcradle 43 which is best seen in Figure 6.

The sub-cradle G5 is laterally movable and bears a prism system having apair of adjacent prisms 44, 64 in line with the objective lens system39. The prism system is such that a small transverse movement of adegree line image projected on to the prism system from the. ring H! onthe glass annulus I1 results in a greatly magnified transverse movementof the degree line in a projection lens system 45 fitted to a maincradle 46 at the outside of the prism system.

Thesub-cradle .43 is carried by the main cradle 45. and is supported fortransverse 51lding movement on two parallel rods 41, 58 disposed oneabove the other in the main cradle 45. A pin I2 is threaded in the maincradle 46 and prevents endwise movement of the upper rod 48 by engaginga co-operating groove '85 (Figure 5). The'upper rod 48 is machined witha coarse-pitch thread .9 engaged by a pin 50, similar to the first pin12 which is threaded in the sub-cradle. Thus rotation of the upper rod28 will produce transverse sliding movement of the sub-cradle 65, so

that the prism system is shifted laterall between the objective lens 35and the projection lens 45.

This movement is effected manually by a control knob 5|; at the frontand to one side of the casing 42. The knob 5| is fixed on the outer endof a shaft 52 which projects through an'opening 53 in the casing 42. Theshaft 52 is supported ina bearing 55 on the main cradle 46 and isconnected at its inner end and to the upper rod 48 by bev lg aringiia Anannular locking knob 55 concentr c with the control knob 5| has a hub 51which screws into the casing52 for clamping together axially a frictiondisc 59 on the hub 51 and a collar 58 on the shaft.

At the other of the casing 4-2 is a second control'knob 55 fitted on aneccentric shaft 6| which extends below the screwed rod and passesthrougha bearing 52 in the main cradle 55. The eccentric shaft 55pivoted at its inner end in the bracket at the back of the casing 12. Anannular locking knob E53 locks the knob 60 and shaft 6! in their setposition in a manner similar 7 to that in which the other locking knob55 locks knob 5| and shaft 52. Rotation of the second control knob 55'has the effect of laterally shifting the main cradle it in front of thebracket 4!. As

the sub-cradle is carried by the main cradle .6, as a consequence boththe projection lens systemtb? and the prism system will be laterallyshifted together.

As'shown in Figure 7,. the external face of the en er P smJ4 n thepr srnsy e is the index 14. The sub-cradle is then locked in position by itsannular control knob 55. 'In order to rotate the table Ill rapidly sothat an image of the zero degree line due to the ring I9 is least in thevicinity of the screen ll, the worm at is disengaged from the worm-wheel80 by rotating the knurled drum B8 and bearing 83 with it, until thetable can be rotated free from the worm 8|. Further rotation of theknurled drum brings the worm 8| again into driving engagement with theworm-wheel so. The bearing 83 is'then locked by screwing up the lockingpin 89, The hand- Wh'cel 95 is pressed inwardly toward the table i untildog 99 is retained in engagement with the radial slot let of thespur-wheel 98 by the springloaded ball 96, The table it is then rotatedby the hand-wheel 95 until the zero degree line image sets convenientlynear the zero pair of lines of the image of the reference scale iii onthe screen ll. In order to move the degree The image into the exactposition the hand-wheel 95 is pulled outwardly from the table is untilthe pinion 93 is retained in engagement with the spur-wheel 93 by thespring-loaded ball 95. This enables the hand wheel 95 to be rotated sothat the degree line'image moves across the screen and sets exactlymid-way between the zero pair of lines of the reference scale 68. By theabove sequence of operations the table is set at the Zero reading.

If the operator desires to rotate the table through an angle of say, 15437 36 from the "zero reading, the above sequence of operations forrotating the table is carried out. Firstly, the Worm BI is disengagedfrom the worm-Wheel 3e and then the table is rotated by hand until theimage of the 15 degree line of the ring is brought into approximatelythe desired position. Thereaiter the worm 8! is again brought intoengagement with the W0li1'l-Whe1 B9 and then the table is rotated by thehandayheel db and direct drive to move the degree line mid-way betweenthe pair of lines of the reference scale image indicating the 40' mark.The sub-cradle is now unlocked by unscrewing the annular control knob 56so that the cradle it can be moved by its control knob until the 7' 35mark of the grjat'icule d5 coincides with the index "M. The sub-cradle33 is again locked by its annular control knob do. The degree line imagehas moved slightly away from its position between the 40' pair of linesduring the movement of the graticule b6, and upon now moving it backagain between the 40 pair of lines by using the handwheel 95 and thereduction drive through the epicycle gear train, the table will havebeen rotated through exactly 15 4'? 36", The reading on the screen itappears as shown in Figure 7.

If desired the table can be locked against rotation by screwing up knobsI69 and lit.

We claim:

l. A rotatable dividing table comprising in combination a base, a tablerotatably mounted thereon, a main circular scale secured to theunderside of the table to rotate therewith, an illuminant therefor, anoptical projection system directed upon the scale, a projection screencarried by the base and positioned to receive an image of main scalemarkings from the optical projection system, a prismcarrying cradle, apair of similar prisms mounted in the cradle, reversed in relation toone another and located in the path of the light beam projecting saidimage to displace the same on the screen, said prisms being cantedrelatively to one another, means to move the cradle with the prismsbodily transversely across the light beam and so vary the displacementof said image, a secondary scale associated with said prisms to movetherewith and located in the path of the light beam so as to beprojected upon the screen along with the image of main scale markings,and index means visible upon the projection screen for the main andsecondary scales and into registration with which the markings of saidscales can be adjusted by rotation of said rotatable table and movementof said prisms, respectively.

2. A rotatable dividing table as claimed in claim 1 having a referencescale in addition to the main and secondary scales, which referencescale is visible upon the projection screen and "comprises a series ofmarkings into registration with any one of which. a main scale markingcan be adjusted.

A rotatable dividing table as claimed in claim 1 wherein a transparentreference scale member is located in the path of the light beam so as tobe projected upon the projection screen along with the main scale andsecondary scale markings.

4. A rotatable dividing table as claimed in claim 1 wherein a projectionlens of the optical system is mounted upon a laterally movable maincradle and the prisms system mounted upon a sub-cradle carried by themain cradle so as to be displaceable thereon and separate adjustingmeans are provided for moving the sub-cradle u on the main cradlelaterally in one direction and the prisms system upon the cradle in adirection at right angles thereto.

In a setting device for a movable member the combination of a mainmovable scale movable in association with said member, an illuminanttherefor, an optical projection system di-= rected thereon, a projectionscreen positioned to receive an image of main scale markings from theoptical projection system, a prism-carrying cradle, a pair of similarprisms inimovably secured in the cradle so that they are reversed inrelation to one another and canted relatively to one another, that is,their internally opposed faces are not parallel, the cradle beinglocated so that the light beam passes through the prisms, means to movethe cradle with the prisms bodily transversely across the light beam andso vary the displacement of said image, a secondary scale to indicatemovement of said prisms, and index means visible upon the screen intoregistration with which the image of the main scale markings can beadjusted by said movement of the prisms, said secondary scale being solocated in the light beam of the optical projection system that itsimage is projected on the projection screen along with the image of themain scale markings.

A rotatable dividing table device comprising a base, a table rotatableon the be so, a main movable scale secured to the rotatable table, and asetting device for the rotatable table, said setting device including anilluminant for said main movable scale, an optical projection systemdirected thereon, a projection screen carried by said base andpositioned to receive an image of main scale markings from the opticalprojection system, a prism-carrying cradle, a pair of similar prismsimmovably secured in the cradle so that they are reversed in relation toone another and canted relatively to one another, that is, theirinternally opposed faces are not parallel, the cradle being located sothat the light beam passes through the prisms, means to move the cradlegraved in its lower half with a' g'raticule 66 comprising a lateralminute-second scale having a range of minutes from 0' to 10. The lengthof the graticule 66 is such that the graticule spans a 10-minuteinterval of the table setting image produced by laterally shifting theprism and lens system. Each minute division of the graticule 6B ismarked with the numerical reading, and the divisions are subdivided bytwo second lines of which the 10 second lines are marked with numericalreadings. Fixed on the main cradle 46 behind the objective lens 39 andimmediately in front of the graticule 66 is a reference scale 6'!bearing a single-degree scale 68 marked with 10- minute division lineseach having a numerical reading. For convenience of sightingeachdivision on this scale is marked by a pair of parallel lines setclose together. The reference scale 61 also bears a central index 14.

Referring more particularly to Figures 2 and 7, an image projectedforwardly by the projection lens 45 is reflected back and upwards by aninclined mirror 69 in front of the lens 35 on to a second inclinedmirror H! which is mounted in the top of the casing 42 and thence theimage is reflected on to the back of the ground-glass screen "II fittedto the top and front of the casing 42 in a position such that it isslightly tilted back for convenience of reading measurements of theprojected ring l9 and scales 56, 68.

With the angular setting of the table [0 at zero, for example, thescreen H displays an image of the zero-degree line from the ring 19, set

between the zero pair of lines in the image of the reference scale 61and below the reference scale the fixed central index mark 14 is alignedwith the zero line on a portion of the image of the graticule 66.

For accurate control in setting the table 50, it is preferred to employa worm 3! and wormwheel drive incorporating an epicyclic gear forproducing a low-geared drive 80 to effect exact setting of the table. Inthe preferred construction of control means (Figures 1A, 8 and 9) aworm-wheel 80 on the table if] is driven by a worm M on a shaft 82carried in a bearing 83 which is eccentrically mounted for rotation in ahousing M extending forwardly at a tangent to the base if. Stops 85, 86on the housing engage an annular groove 81 and longitudinal groove l8?respectively in the bearing to prevent axial movement of the bearing 83and limit its rotational movement. At its forward end the bearing 83projects from the housingas and is there fitted with a knrrled drum 03by which the bearing 83 is rotated in one or other direction so as todisplace the shaft 82 laterally and thereby throw the worm 85 in and outof engagement with the worm-wheel 86. When the worm 8i is disengaged ittakes up the position shown by chain-lines in Figure 1A, the table illis free to be rotated by hand for quick positioning to a rough angularsetting. The bearing 83 is locked in its set position by a locking pin89 with a handle iii! which screws into the housing 84 and at its innerend 65 reading on the screen prior to rotating the table through adesired angle, an operator combears down on a clamping washer 3iengaging the bearing- 83. 7

Fixed within the knurled drum is an externally-toothed gear ring 92which is in constant mesh with a pinion 93 carried on a spindle 94 atthe rim and inside of a hand-whee This pinion 93 is diametrically splitand spring loaded to relieve back-lash in the gear teeth. The handwheel95 is carried on the projecting outer end of the worm shaft 32 on whichit is free to rotate wheel 98.

and also has alimited axial movement. A spring {loaded ball in thehand-wheel snaps into one or other of two annular grooves 91 in theshaft 32 when the hand-wheel 95 is shifted along the shaft 82 to aninner or an outer position as shown respectively in Figure 8 and Figure9. Fixed to the shaft 82 at the inside of the handwheel 95 there is aspur-wheel 98 which the pinion 93 engages when the hand-wheel 95 ispulled out, but which is disengaged from the pinion 95 when thehand-wheel 95 is pushed inwards. At the inner position of the hand-wheel95 a springloaded dog 95 at the back of the hand-wheel 95 is urgedrearwardly into engagement with a radial. slot its at the outer face ofthe spur-wheel '98 whereby the hand-wheel 95 and spur wheel 98 arelocked together for rotation together as 'a unit.

that the worm-shaft 82 rotates at the same speed as the hand-wheel. Ifthe worm BI and wormwheel 8d are geared 300:1, then an overall gearratio of this amount is obtained forcoarse adjust- 'ment of the table.

On pulling out the hand-wheel 95 the dog 99 is disengaged and anepicyclic gear train will be formed by the gear ring 92, pinion 93 andspur- Rotation of the hand-wheel $5 will cause the pinion 93 to ridearound and rotate on the fixed gear ring 92 acting as a sun-wheel, and

the rotation of the'pinion 93 will drive the wormshaft 82 through thespur-wheel 93. If the gear ring 92 spur-wheel 83 are formed respectivelywith 19 and 50 teeth, the epicyclic gear gives a gear reduction of 50:1,so that with the worm ratio of 300:1 a reduction of 15,000z1 is affordedfor precise adjustment of the table it.

In order to lock the table H8 at its angular setting, the table isfitted near its perimeter with a concentric skirt l0l (Figure 2) ridingover a fixed ring Hi2 upstanding from the base 52. The skirt liil housesa circle of spaced rollers are each disposed radially of the skirt Filland fitted in a hole Hi4 within the skirt liH so as to slide freely inthe hole ills along its axis without lateral play.

A radial hole I05 in the base of the dividing table :houses a slidingthrust rod 506 Whose inner end bears on a pad till which spans the outerends of several rollers 03 in the skirt Edi. A screwed spindle W8co-axial with the thrust rod m5 is rotatable by a knob 109 for pushingthe thrust rod Hi6 inwards in order to force the pads 10'! against theseveral rollers Hit. The rollers 13 are in consequence clamped betweenthepad fill and the fixed base ring m2 and the skirt iiii and table Itare thus clamped against rotation without any pressure being applied tothe table bearing M. A second knob Mil (Figure 1B) for clamping thetable Iii is similar to knob I09 and is disposed further round the baseat the same level.

In order to set the table It! initially at a zero mences by moving themain cradle 45 laterally by rotating its control knob E0 until an imageof the reference scale 6'! appears centrally on the screen H.

with the prisms bodily transversely across the light beam and so varythe displacement of said image, a secondary scale to indicate movementof said prisms, and index means visible upon the screen, intoregistration with which the image of the main scale markings can beadjusted by said movement of the prisms, said secondary scale being solocated in the light beam of the optical projection system that itsimage is projected on the projection screen along with the image of themain scale markings.

CORNELIUS FRANK DIE'I'RICH. HARRY JOHN SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Number 15 813,311 870,687 574,295 615,183

Name Date Wild Sept. 16, 1924 Guild Aug. 28, 1928 Fassin Sept. 25, 1934Patrick Mar. 17, 1942 Larsen et a1 Nov. 28, 1944 Decker et a1. Jan. 23,1945 Becker etal June 17, 1947 Turrettini Mar. 29, 19,49 Godfrey et a1.Aug. 30, 1949 FOREIGN PATENTS Country Date France Feb. 22, 1937 FranceDec. 22, 1941 Great Britain Dec. 31, 1945 Great Britain Jan. 3, 1949

